**Core Concept:**
The liver plays a crucial role in the body's detoxification process, particularly in the clearance of ammonia, a toxic substance produced as a byproduct of protein digestion. Hepatic cells, known as hepatocytes, are responsible for converting ammonia into less harmful substances like glutamine, alanine, and urea.

**Why the Correct Answer is Right:**
Ammonia is primarily supplied to the liver via the portal vein, specifically the portal triad formed by the confluence of the superior mesenteric vein, portal vein, and hepatic artery. This structure facilitates the direct delivery of nutrients, oxygen, and waste products, including ammonia, to the liver.

**Why Each Wrong Option is Incorrect:**
A. Hepatic artery (Option A) carries oxygenated blood to the liver, but it does not contribute to ammonia transport.
B. Hepatic vein (Option B) is responsible for removing waste products from the liver, not supplying them.
C. The hepatic artery and vein (Option C) are both involved in delivering oxygen and removing waste products, but not specifically ammonia.
D. The common bile duct (Option D) transports bile produced in the liver, not ammonia.

**Clinical Pearl / High-Yield Fact:**
The portal triad ensures efficient nutrient and waste product distribution within the liver, highlighting the importance of a well-functioning circulatory system for liver health and detoxification capabilities. This concept is crucial for understanding liver diseases like portal hypertension and liver failure, where abnormalities in the portal triad can lead to impaired detoxification processes and clinical manifestations.

**Correct Answer:**
A. Portal vein (Ammonia supply)

Explanation: The correct answer is the portal vein (Option A), which carries deoxygenated blood containing ammonia from the intestines and pancreas to the liver, where it is then processed by hepatocytes.